A light emitting element has been applied in various fields because of low electrical power consumption. For example, a light emitting diode (hereinafter can be referred to as LED for short) can work not only as a monochromatic LED emitting light in red, green, blue or the like, but also as a white LED by providing a fluorescent material on a blue LED; therefore, LEDs, with the help of improvement on luminance thereof, have been widely spread in application over many fields such as a light source for an electric display board, a backlight source for a portable telephone, a personal computer and the like.
An LED emitting blue light has been generally manufactured by forming an electrode for p type and an electrode for n type onto the surface of the GN-based compound semiconductor which is laminated on a insulating substrate consisting of sapphire. Such an LED emitting blue light has been in more cases employed as a so-called flip-chip type light emitting element, which is surface mounted at the electrodes. In such a flip-chip type light emitting element, the surface of the sapphire substrate can be a light emitting surface by mounting the element so as to the substrate facing to a light emitting direction because sapphire has translucency. Recently, a light emitting element chip has been mounted on a substrate of equipment, and in addition, as a useful light emission source, a complex light emitting element has been employed. In the complex light emitting element, the light emitting element chip is mounted, for example, on a submount element for electrostatic protection with a Zener diode.
Such a complex light emitting element has a structure that a flip chip type blue light emitting element is conduction-mounted on a submount, which is conduction-mounted on amounting substrate incorporated in electronic equipment or the like. Conventionally, a silicon substrate has been used as a submount, whereas there has been a problem that a complex light emitting element is reduced in luminance thereof since the silicon substrate absorbs light in the wavelength range of from 450 nm (blue) to 560 nm (green) emitted from an LED.
Therefore, a proposal has been made on a complex light emitting element having a mounting surface for a light emitting element, which surface is made from a white insulator such as alumina, without such a problem (see Japanese Patent Application Laid-Open No. 2003-60243).
An aluminum oxide sintered body in white color of which an insulating substrate of Japanese Patent Application Laid-Open No. 2003-60243 is constituted has a property that a reflectance is 50% or more in the range of from 350 to 560 nm in wavelength, while, on the other hand, having a property of a thermal conductivity of about 20 W/m·K, which is relatively small, which makes it hard to radiate heat from the light emitting element to outside, causing a possibility of damage in the light emitting element to be revealed.